Device for discharging static electricity

ABSTRACT

A device for discharaging static electricity protects an internal circuit against an electrostatic current. The device includes a discharge part which is connected between an input/output pad and a ground voltage line to form a discharge path discharging an electrostatic current introduced from an input/output pad; and an amplification circuit which is connected in parallel with the discharge part and supplies a sense amplification signal generated by amplifying the electrostatic current as a control signal of the discharge part.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Korean patent applicationnumber 10-2006-061588 filed on Jun. 29, 2006, which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, and moreparticularly, to a device for discharging static electricity, which canprotect an internal circuit against an electrostatic current.

Generally, electrostatic discharge (ESD) is a rapid flow of electriccurrent that takes place when two mutually insulated objects withsignificantly different potentials come into direct contact with eachother.

When an ESD is introduced to a semiconductor device, circuits inside thedevice can be damaged. In order to protect internal circuits, mostsemiconductor devices include one or more ESD protection units betweenan externally located electrical contact pad for the device and internalcircuits.

A diode, a metal oxide silicon (MOS) transistor and a silicon controlledrectifier (SCR) are all used as ESD protection units.

An SCR is an ESD protection unit, which can receive a high ESD currentper unit area of its semiconductor junctions and which has low junctioncapacitance and low operating resistance. However, an SCRdisadvantageously has a higher operation voltage than other ESDprotection units.

FIG. 1 illustrates a conventional prior art circuit 10 for dischargingstatic electricity.

Referring to FIG. 1, in order to discharge an electrostatic currentintroduced to an input/output pad 102 to a ground voltage line (or VSS:104), the conventional circuit 10 for discharging static electricityuses a silicon controlled rectifier (SCR) having a relatively highoperation voltage as a discharge part between the input/output pad 102and the VSS 104. In order to reduce the operating voltage of the SCR110, the circuit 10 also includes an NMOS transistor 120 as a driveelement, connected between the input/output pat 102 and the SCR 110, andwhich detects a drive current 12 and then supplies it to the SCR 110.Therefore, the device 10 operating voltage can be reduced to a breakdownvoltage of the NMOS transistor 120, while ESD effect of the SCR 110 ismaintained.

In the device shown in FIG. 1, the SCR 110 is not operated until theelectrostatic voltage reaches the brakedown voltage. Thus, a circuitinternal to a semiconductor device might not be adequately protectedfrom static electricity at an initial or relatively low voltage range ofan electrostatic pulse.

SUMMARY OF THE INVENTION

The present invention provides a device for discharging staticelectricity, which reduces the operation voltage and rapidly operates atan initial range of an electrostatic pulse, thereby protecting aninternal circuit more effectively.

The present invention also provides a device for discharging staticelectricity, which amplifies an introduced electrostatic current andthen provides it as a control signal of the SCR, thereby safelyprotecting the internal circuit at the initial range of staticelectricity.

According to an aspect of the present invention, there is provideddevice for discharging static electricity, comprising a discharge partwhich is connected between an input/output pad and a ground voltage lineto form a discharge path discharging an electrostatic current introducedfrom an input/output pad; and an amplification circuit which isconnected in parallel with the discharge part and supplies a senseamplification signal generated by amplifying the electrostatic currentas a control signal of the discharge part.

In the aforementioned aspect of the present invention, the dischargepart is a SCR element.

In addition, the discharge part comprises a first resistor and a NPNbipolar transistor which are connected in series between theinput/output pad and the ground voltage line; and in parallel thereto, aPNP bipolar transistor and a second resistor which are connected inseries between the input/output pad and the ground voltage line, whereina first node which is commonly connected with the first resistor and theNPN bipolar transistor is connected with a base of the PNP bipolartransistor, and a second node which is commonly connected with the PNPbipolar transistor and the second resistor is connected with a base ofthe NPN bipolar transistor, thereby forming a latch, and the dischargepart is operated when the sense amplification signal amplified in theamplification circuit is supplied to the second node.

In addition, the amplification circuit comprises a drive control partwhich comprises a first NMOS transistor of which a drain is connectedwith the input/output pad and a gate is connected with the second node,and a resistor of which one end is connected with the ground voltageline and the other is connected with a source of the first NMOStransistor, and which detects a detection voltage generated at a thirdnode commonly connected with the first NMOS transistor and the resistor;and a drive part which comprises a second NMOS transistor of which adrain is connected with the input/output pad and a source is connectedwith the second node and a gate is connected with the third node, andwhich is operated by the detection voltage to generate the senseamplification signal amplified corresponding to an electrostatic currentand provide it to the second node.

In addition, the amplification circuit is constructed such that the gateof the first NMOS transistor is connected with the source of the secondNMOS transistor, and the gate of the second NMOS transistor is connectedwith the source of the first NMOS transistor, and the first and secondNMOS transistors mutually form a latch to amplify the signal.

In addition, the amplification circuit comprises a drive control partwhich comprises a NMOS transistor of which a source is connected withthe ground voltage line and a gate is connected with the second node,and a resistor of which one end is connected with the input/output padand the other is connected with a drain of the NMOS transistor, andwhich detects a voltage drop generated at a fourth node commonlyconnected with the NMOS transistor and the resistor by the electrostaticcurrent; and a drive part which comprises a PMOS transistor of which adrain is connected with the input/output pad and a source is connectedwith the second node and a gate is connected with the fourth node, andwhich is operated by the voltage drop to generate the senseamplification signal amplified corresponding to an electrostatic currentand provide it to the second node.

In addition, the amplification circuit is constructed such that the thegate of the NMOS transistor is connected with the source of the PMOStransistor, and the gate of the PMOS transistor is connected with thedrain of the NMOS transistor, and the NMOS transistor and the PMOStransistor mutually form a latch to amplify the signal.

In addition, the device is connected between an external power voltageline and the ground voltage line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a prior art conventional device fordischarging static electricity.

FIG. 2 is a circuit diagram of a device for discharging staticelectricity according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of a device for discharging staticelectricity according to anthor embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 2 is a circuit diagram of a device for discharging staticelectricity according to an embodiment of the present invention. Adischarge part 210 and an amplification circuit 220 are connected inparallel to each other, and connected between an input/output pad 202and a ground voltage line (or VSS) 204. The discharge part 210 iscontrolled by a sense amplification signal of the amplification circuit220.

In order to discharge an electrostatic current to the VSS 204, thedischarge part 210, which is embodied as a SCR, is constructed such thata resistor R1 and an NPN bipolar transistor T1 are connected in serieswith each other between the input/output pad 202 and the VSS 204, and inparallel with a PNP bipolar transistor T2 connected in series with aresistor R2 and which are themselves also connected between theinput/output pad 202 and the VSS 204.

A common connection node A of the resistor R1 and the collector of NPNbipolar transistor T1, is connected to the base of PNP bipolartransistor T2. A common connection node B of the collector of PNPbipolar transistor T2 and the resistor R2, is connected to the base ofthe NPN bipolar transistor T1. Connected as they are in FIG. 2,transistors T1 and T2 and the resistors R1 and R2 form a latch.

The sense amplification signal of the amplification circuit 220, isprovided to the node B of the discharge part, and the amplificationcircuit 220 is provided with a drive control part 222 and a drive part224.

The drive control part 222 includes a NMOS transistor N1, the drain ofis connected to the input/output pad 202 and a drain and a gate isconnected with the node B, and a resistor R3 of one end is connected toa source of the NMOS transistor N1 and the other end is connected to theVSS 204, and applies a detection voltage detected at a common connectionnode C of the NMOS transistor N1 and the resistor R3 to the drive part224.

The drive part 224 includes a NMOS transistor N2, the drain of which isconnected with the input/output pad 202 and a source is connected to thenode B and a gate is connected to the node C. The drive part 224 isturned on by the detection voltage of the drive control part 222 andapplies the sense amplification signal generated by amplifying theelectrostatic current from the input/output pad 202 to the node B,thereby reducing the operation voltage of the discharge part 210 andthus causing a fast discharge operation.

Hereinafter, the operation of the device for discharging staticelectricity according to the embodiment of the present invention will bedescribed, referring to FIG. 2. If an electrostatic pulse is introducedto the input/output pad 202, a voltage of the node C is raised by acurrent through the NMOS transistor N1 and the resistor R3 of the drivecontrol part 222, and the gate voltage of NMOS transistor N2 of thedrive part 222 is regulated by the increased voltage. Current applied tothe discharge part 210 can thus be regulated.

That is, the larger the amount of current passing thorugh the NMOStransistor N1 of the drive control part 222 is, the more the voltage ofnode C is increased. Thus, a drive current flowed to the node B throughthe NMOS transistor N2 is increased. Further, the amount of currentpassing through the NMOS transistor N1 of the drive control part 222 isregulated by the voltage provided at the NMOS transistor N2 of the drivepart 224. In other words, if the drive current supplied through the NMOStransistor N2 of the drive part 224 is large, the gate voltage of theNMOS transistor N1 of the drive control part 222 is increased.Therefore, the current passing through the NMOS transistor N1 isincreased.

As described above, the current at the drive control part 222 and thedrive part 224 have the relationship of a positive feedback. Therefore,when a high pulse at the initial state of static electricity is appliedthrough the input/output pad 202, the amplification circuit 220amplifies a very small amount of current generated from the NMOStransistor N1 of the drive control part 222 and the NMOS transistor N2of the drive part 224 to generate the sense amplification signal andthen provides it to the discharge part 210, thereby rapidly operatingthe discharge part 210 and thus protecting an internal circuit againstthe static electricity.

FIG. 3 is a circuit diagram of a device for discharging staticelectricity according to anthor embodiment of the present invention.

Referring to FIG. 3, in the device for discharging static electricityaccording to anthor embodiment of the present invention like the deviceof FIG. 2, a discharge part 310 and an amplification circuit 320 areconnected in parallel with each other and between an input/output pad302 and a ground voltage line (or VSS) 404, and the discharge part 310is controlled by a sense amplification signal of the amplificationcircuit 320.

The discharge part 310 has the same structure as the discharge part 210of FIG. 2. In order to discharge an electrostatic current to VSS 304, aresistor R1 and an NPN bipolar transistor T1 are connected in seriesbetween the input/output pad 302 and the VSS 304, and in parallelthereto, a PNP bipolar transistor T2 and a resistor R2 are connected inseries between the input/output pad 302 and the VSS 304.

A common connection node A of the resistor R1 and the NPN bipolartransistor T1 is connected to a base of the PNP bipolar transistor T2,and a common connection node B of the PNP bipolar transistor T2 and theresistor R2 is connected to the base of the NPN bipolar transistor T1,thereby forming a latch.

The sense amplification signal of the amplification circuit 320 isprovided to the node B of the discharge part 310, and the amplificationcircuit 320 is provided with a drive control part 322 and a drive part324.

The drive control part 322 includes a NMOS transistor N3 of which asource is connected with the VSS 304 and a drain and a gate is connectedwith the node B, and a resistor R4 of one end is connected to theinput/output pad 302 and the other end is connected to the a drain ofthe NMOS transistor N3, and detects a voltage drop generated at the acommon connection node D of the resistor R4 and the NMOS transistor N3by the electrostatic current and applies it to the drive part 324.

The drive part 324 includes a PMOS transistor P1 of which a drain isconnected with the input/output pad 302 and a source is connected to thenode B and a gate is connected to the node D. The drive part 224 isturned on by the detection voltage of the drive control part 322, whichis applied to the gate, and applies the sense amplification signalgenerated by amplifying the electrostatic current from the input/outputpad 302 to the node B, thereby reducing the operation voltage of thedischarge part 310 and thus causing a fast discharge operation.

Hereinafter, the operation of the device for discharging staticelectricity according to another embodiment of the present inventionwill be described, referring to FIG. 3. If an electrostatic pulse isintroduced to the input/output pad 302, a voltage drop occurs at node Dby the current through the resistor R4 and the NMOS transistor N3 of thedrive control part 322. The gate voltage of the PMOS transistor P1 ofthe drive part 324 is regulated by the dropped voltage and thus anamount of current applied to the discharge part 310 can be regulated.

That is, the larger the amount of current passing through the NMOStransistor N3 of the drive control part 322 is, the more the drivecurrent flowed through the PMOS transistor P1 of the drive part 324 tothe node B is increased. Thus, a drive current flowed to the node Bthrough the PMOS transistor P1 of the drive part 324 is increased.

Further, the amount of current passing through the NMOS transistor N3 ofthe drive control part 322 is regulated by the voltage provided at thePMOS transistor P1 of the drive part 324.

In other words, if the drive current supplied through the PMOStransistor P1 of the drive part 324 is large, the gate voltage of theNMOS transistor N3 of the drive control part 322 is increased.Therefore, the current passing through the NMOS transistor N3 isincreased.

As described above, the current at the drive control part 322 and thedrive part 324 have the relationship of a positive feedback. Therefore,when a high pulse at the initial state of static electricity is applied,the amplification circuit 320 amplifies a very small amount of currentgenerated from the NMOS transistor N3 of the drive control part 322 andthe PMOS transistor P1 of the drive part 324 and generates the senseamplification signal.

The the amplification circuit 320 amplifies the electrostatic currentintroduced through the input/output pad 302 to generate the senseamplification signal and then provides the sense amplification signal tothe SCR 310, thereby rapidly operating the discharge part 210 and thusprotecting an internal circuit against the static electricity.

Therefore, the present invention provides a device for dischargingstatic electricity, which reduces the operation voltage and rapidlyoperates at an initial range of an electrostatic pulse, thereby safelyprotecting an internal circuit.

Further, the present invention also provides a device for dischargingstatic electricity, which amplifies an introduced electrostatic currentand then provides it as a control signal of the SCR, thereby safelyprotecting the internal circuit at the initial range of staticelectricity.

1. A device for discharging static electricity, comprising: a dischargepart which is coupled between an input/output pad and a ground voltageline to form a discharge path, discharging an electrostatic currentintroduced to the input/output pad; and an amplification circuit, whichis coupled in parallel with the discharge part and which supplies asense amplification signal that is generated by amplifying theelectrostatic current as a control signal of the discharge part, whereinthe amplification circuit comprises: a drive control circuit, whichcomprises a first NMOS transistor, the drain of which is coupled to theinput/output pad and a gate is coupled to a first node, and a firstresistor of which one end is coupled to the ground voltage line and theother is coupled to a source of the first NMOS transistor, and whichdetects a detection voltage generated at a second node commonlyconnected with the first NMOS transistor and the first resistor; and adrive part which comprises a second NMOS transistor, the drain of whichis coupled to the input/output pad and a source is coupled to the firstnode and a gate is coupled to the second node, and which is operated bythe detection voltage to generate the sense amplification signalamplified corresponding to an electrostatic current and provide it tothe first node.
 2. The device according to claim 1, wherein thedischarge part is a silicon controlled rectifier (SCR).
 3. The deviceaccording to claim 2, wherein the discharge part comprises a secondresistor and a NPN bipolar transistor which are coupled in seriesbetween the input/output pad and the ground voltage line; and inparallel thereto, a PNP bipolar transistor and a third resistor whichare coupled in series between the input/output pad and the groundvoltage line, wherein a third node which is commonly coupled with thesecond resistor and collector of the NPN bipolar transistor is coupledwith a base of the PNP bipolar transistor, and the first node which iscommonly connected with the collector of the PNP bipolar transistor andthe third resistor is connected with a base of the NPN bipolartransistor, thereby forming a latch, and the discharge part is operatedwhen the sense amplification signal amplified in the amplificationcircuit is supplied to the first node.
 4. The device according to claim1, wherein the amplification circuit is constructed such that the gateof the first NMOS transistor is coupled to the source of the second NMOStransistor, and the gate of the second NMOS transistor is coupled to thesource of the first NMOS transistor, and the first and second NMOStransistors mutually form a latch to amplify the signal.
 5. The deviceaccording to claim 1, wherein the device is connected between anexternal power voltage line and the ground voltage line.
 6. A device fordischarging static electricity, comprising: a discharge part which iscoupled between an input/output pad and a ground voltage line to form adischarge path, discharging an electrostatic current introduced to theinput/output pad; and an amplification circuit, which is coupled inparallel with the discharge part and which supplies a senseamplification signal that is generated by amplifying the electrostaticcurrent as a control signal of the discharge part, the amplificationcircuit comprising: a drive control part which comprises a NMOStransistor of which a source is coupled to the ground voltage line and agate is coupled to a first node, and a resistor of which one end iscoupled to the input/output pad and the other is coupled to a drain ofthe NMOS transistor, and which detects a voltage drop generated at asecond node commonly coupled to the NMOS transistor and the resistor bythe electrostatic current; and a drive part which comprises a PMOStransistor of which a drain is coupled to the input/output pad and asource is coupled to the first node and a gate is coupled to the secondnode, and which is operated by the voltage drop to generate the senseamplification signal amplified corresponding to an electrostatic currentand provide it to the first node.
 7. The device according to claim 6,wherein the amplification circuit is constructed such that the gate ofthe NMOS transistor is coupled to the source of the PMOS transistor, andthe gate of the PMOS transistor is coupled to the drain of the NMOStransistor, and the NMOS transistor and the PMOS transistor mutuallyform a latch to amplify the signal.